Confusion on That when followed by "x of y"

[Everything OR Nothing]

This is GMAT PREP free Question.

In the mod-1920s the Hawthorne Works of the Western Electric Company was the scene of an intensive series of experiments that would investigate changes in working conditions as to their effects on workers’ performance.
A. that would investigate changes in working conditions as to their effects on workers’ performance
B. investigating the effects that changes in working conditions would have on workers’ performance
C. for investigating what the effects on workers’ performance are that changes in working conditions would cause
D. that investigated changes in working conditions’ effects on workers’ performance
E. to investigate what the effects changes in working conditions would have on workers’ performance

In the above question Correct answer is B
In D I understand Conditions's effect is not good.
But Choice D is wrong for another reason as per Ron's Rule in one of the discussion( if I remember correctly ) that says in structure such as "x of y that " that refers to x always .So in Choice D " that" is referring to series , making the choice D illogical : we should mean experiments instead of series in this context.

BUT take a look at the below question

In attempting to solve the problems caused by a lowering of the price of oil, oil companies operating in the North Sea have taken a variety of approaches, which includes their reducing employment, using new tech to pump oil more efficiently from smaller fields, and finding innovative ways to cut the cost of building and operating platforms.
B) which includes reducing employment, using new tech to be more efficient in pumping oil
C) which include reducing employment, using new tech to pump oil more efficiently
Correct choice is C.

EXPLANATION:

• The bouquet of flowers that is kept on the table is already sold.
• The bouquet of flowers that are extraordinarily fragrant is kept on the table.
From the above sentences, we understand that the number of verb depends upon the subject it associates with. The context and the intended meaning of the sentence drives the modification of "that" and hence the use of correct verb.


SO what is exactly the rule on construction such as "X OF Y THAT" ? Kindly help. Thanks

[RonPurewal]

the point is that you have to read the sentence, think about what it means, and then use old-fashioned common sense to determine which thing is the subject.

here's an "activity". pick a verb for each one. then scroll down for the answers.

1/
I wrote a book on forensic techniques that ( was / were ) reviewed favorably in the New York Times Review of Books.

2/
I wrote a book on forensic techniques that ( is / are ) now being revolutionized by cutting-edge science, so I will have to produce a new edition soon.

[RonPurewal]

1/
"was"
...because the NYT Review of Books contains reviews of, well, books. a book review is not going to review forensic techniques.


2/
"are"
...because it makes perfect sense to say that forensic techniques are "being revolutionized by cutting-edge science", whereas it makes no sense whatsoever to say the same thing about a book.